Magnetoelastic transducer



Oct. 16, 1956 W. T. HARRIS MAGNETOELASTIC TRANSDUCER Filed Feb. 23, 1955 FIG. l.

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ifmmmwlf United States Patent O MAGNETOELASTIC TRANSDUCER Wilbur T. Harris, Southbury, Conn., assignor to The Harris Transducer Corporation, Woodbury, Conn., a corporation of Connecticut Application February 23, 1955, Serial No. 490,043

13 Claims. (Cl. S10-26) My invention relates to electromagnetic transducers of the magnetoelastic variety disclosed and discussed in detail in my copending patent application, Serial No. 383,563, filed October 1, 1953.

In said copending application, I discussed the relative merits of various basic transducer types and pointed out the relatively high conversion efficiency achievable with the magnetoelastic transducer. Among the forms disclosed were several employing a consolidated stack of like laminations, each lamination incorporating all the basic elements of the transducer. Such transducers rely primarily on the contraction which results from magnetic forces at a gap in the central part of the flux path excited by a coil. Contraction is accompanied by a resilient elongation and by resonance between particular parts of the laminations. The magnetoelastic principle is to be clearly distinguished from any purely magnetostrictive effect, in that the magnetostrictive effect relies solely upon the material itself, rather than on magnetic forces contributed at a gap. In spite of the higher conversion etliciency obtainable with the structures disclosed in said patent application, the full potential of the magnetoelastic effect could not be achieved with those particular structures.

It is, accordingly, an object of the invention to provide an improved magnetoelastic transducer-element construction.

It is another object to provide a magnetoelastic transducer lamination of inherently greater energy-conversion eiciency than heretofore.

It is a further object to provide a magnetoelastic lamination with particular configuration of slots, so as to define mass areas which can mechanically react with each other to enhance the magnetoelastic effect.

It is a specific object to achieve the above objects with a structure which can couple the reacting mass areas to the basic magnetoelastic structure with high mechanical advantage, thereby achieving high power capacity,

Other objects and various further features of novelty and invention will be pointed out or will occur to those skilled in the art from a reading of the following specification in conjunction with the accompanying drawings. In said drawings, which show, for illustrative purposes only, preferred forms of the invention:

Fig. l is a cross-sectional view of a transducer incorporating features of the invention and revealing the plan view of one of the laminations of the core thereof;

Figs. 2 and 3 are drawings schematically suggesting two alternative simplified functional equivalents, to explain the principal mode of operation of the device of Fig. l; and

Fig. 4 is a view similar to Fig. l but illustrating a modification.

Briefly stated, my invention contemplates an improved laminated magnetoelastic transducer construction characterized by higher conversion efliciency than heretofore and incorporating, as an integral part of each lamination, additional mass areas which may react with the basic magnetoelastic portion of the lamination in order to enhance the conversion efficiency and power-handling capacity. The means for coupling the magnetoelastic portion of the lamination to the reacting mass portions is inherently characterized by high mechanical advantage.

Referring to Fig. l of the drawings, my improved transducer is seen to comprise a consolidated stack of like laminations 10, each of which may be a single integral sheet of non-critical ferromagnetic material, such as silicon steel. The lamination may be of proportions which are rectangular and hence characterized by symmetrical longitudinal and transverse axes. The lamination may be formed with two like symmetricaly located and longitudinally spaced winding openings 11; after the stack of laminations 10 is consolidated, the turns of winding means 12 are passed through the openings 11 so as to provide electromagnetic coupling to the flux path between the openings 11.

The structure thus far described may be viewed as having two outer legs 13-14 connecting transversely opposed mass areas 1S16, which extend centrally toward each other to define a center leg. The center leg is slotted by a thin opening extending between winding openings 11, thereby defining a flux gap 17 between poles at the center leg. Upon excitation of the winding in openings 11, flux is circulated generally in two symmetrical paths, designated by dashed arrows 18-19 around the respective openings 11. The proportions of the described parts of the laminations 10 are preferably such that the minimum width W of each flux path shall be substantially one-half the effective length of the ux gap 17.

Upon excitation of the described structure, the outer legs 1314, which serve to space the transversely opposed mass areas 15-16, will in effect constitute spring means yieldably connecting the transversely opposed mass areas 15-16, and with each contraction or expansion of the gap, due solely or primarily to magnetic forces at the gap, these outer spring legs 13-14 will permit transverse excursions of the mass areas 15-16. At resonance, the conversion eiciency, as between electricenergy input to the coil 12 and mechanical-displacement output at elements 15--16, is relatively high, and purely magnetoelastic action is involved.

In spite of the high conversion efliciency described above, I provide means whereby the conversion eiiiciency may be further improved, by employing lamination structure integral with that described. This, in the form shown, comprises two longitudinally opposed mass areas 20-21 connected to the spring means or outer legs 13-14. The preferred arrangement is such that the point of connection between mass areas 2li-21 and the main magnetoelastic lamination body shall be in the central or most (longitudinally) deflected parts of the connecting spring legs 13-14. Also, I prefer that the connection shall be via a neck section 22, of limited width t, compared with the over-all transverse width T of the lamination; to provide further compliance in the coupling between the longitudinally opposed mass areas 20-21 and the connecting members 13-14, I prefer that the neck 22 shall be longitudinally elongated, as suggested by the dimension D, shown of the order of magnitude of the width t of the neck 22.

In order to make maximum use of the available volumedisplaced by the lamination 10, I show the reacting longitudinally opposed mass areas as including massive sideprojections or ears Z3 extending toward the magnetoelas-` tic body and closely spaced therefrom, as suggested byy the dimension d. Finally, in order to preserve correct orientation of all laminations when assembled in a stack, I provide a small reference notch or opening 24, asymmetrically disposed with respect to the lamination body' Y c Y 2,767,338

3 and preferably located remote from 18-19.

The functioning of my improved lamination will be better understood by reference to Figs. 2 and 3, either of which provides a simplified partially equivalent structure. In the arrangement of Fig. 2, the transversely spaced mass areas l-lo are identified by the blocks m2, and the longitudinally opposed mass areas are identified by the blocks mi. Springs 26-27-28-29 are shown one of flux paths interconnecting these masses, and the poles for the gap 17 are shown integrally carried by the masses m2. Thus, the masses mi may be viewed as connected to each other by spring means via the masses m2; alternatively, the masses m2 may bc viewed as connected to each other by spring means via the masses m1. Also, by virtue of the described nature of the basic magnetoelastic element excluding the masses m1 (Ztl-21),'the masses me may be viewed as connected to each other byV spring means (Z6-29, and 27-28), the masses mi being merely connected to central parts of such spring means.

In operation of the Fig. 2 arrangement, contraction and expansion of the gap reflects transverse oscillation of the masses m2 and longitudinal oscillation of the masses mi. The springs provide compliant close coupling between the two oscillating systems leading to a double peaked resonant system, i. e. two resonant frequencies. If thc transverse spread of connections to masses mz is much less than the longitudinal spread of connections bctween masses mz, then the coupling between the magnetoelasirlc structure and the longitudinally resonant structure mi is characterized by good mechanical advantage, in force magnification.

In the simplified version illustrated in Fig. 3, the same masses mi and m2 will be recognized, as will be the Winding l2 at gap 17. Connections between masses are, however, schematically suggested by more or less rigid or resiliently longitudinally elongated tie rods 3i? 3-3Z-SS, pinned to the masses mr-mz. Springs, as at 214-35, may constantly be stressed to ride the rods; these springs suggest resilient opposition to pivotl ing of a rod (3l) with respect to the masses it connects, and this type support will be understood to characterize all connections to the masses ini-m2. in operation, contraction of the gap 17 is accompanied by forced spreading of the masses mi in the longitudinal sense, and expansion of the gap` i7 forcibly draws the masses m1 toward each other; the springs 3ft-35 serve compliantly to couple the resulting modes of oscillation.

it will be seen that, if the proportions of the lamination it! are of the predominantly elongated character shown in Fig. l, then, from the analyses depicted in Fig. 2 and 3, good mechanical advantage inherently characterizes the coupling between the magnetoelastically resonant structure (mz) and the purely mechanically resonant structure (mi).

In Fig. 4, I show a modified construction having preferably the proportions described in connect-ion with Fig. l except for width of the gap between the mass areas 152-16; corresponding parts are identified by the same reference characters, but with primed notation. In Fig. 4, the enlarged cap is filled with a sandwich comprising essentially a slab 4b of permanently magnetized material, such as an iron-oxide ceramic or ferrite. T o provide yieldable support for the ferrite layer 40', I show two thin pressure-release membranes i1-42, as of cork, slightly spacing the pole faces of masses ISL-16' from the ferrite slab 413. Operation lis as described for Fig. l, except that, of course, no polarizing potential need be applied to winding 12.

It will be seen that I have described an improved magnetoelastic-transducer construction characterized not only by the high efficiency inherent in the basic magnetoelastic body buta-lso by yimproved efficiency, by reason of coupling to a further mechanically resonant structure'. By exciting the magnetoelastic device transversely, and by coupling the same with good mechanical advantage to a longitudinally resonant structure, I provide for high power-handling potentialities for radiation into a medium of high acoustic impedance.

While I have described the invention in detail for the preferred forms shown, it will be understood that modifications maybe made Within the scope of the invention as defined in the claims which follow.

I claim:

l. In a transducer of the character indicated, a magnetic core comprising a consolidated stack of like laminations of ferromagnetic material, each lamination including three longitudinally spaced legs joined to cach other at opposite transverse ends and defining openings between legs, the center leg having a gap therein of width substantially less than the width of said center leg but sufticient to permit free oscillation of the poles at said gap, a winding passing through said openings, and a pair of longitudinally opposed mass areas connected symmetrically to the respective outer legs of said laminations.

2. A transducer according to claim l, and including permanently magnetized means supported in said gap.

3. A transducer lamination, comprising a single sheet 0f ferromagnetic material having two longitudinally spaced like and symmetrically located winding openings therein, said sheet having a thin elongated open flux gap communicating with both said winding openings, thereby defining a pair of transversely opposed mass arcas including the poles of said gap, said winding openings being located within the longitudinal limits of said sheet, thereby defining integral connecting legs between the outer limits of said mass areas, and a pair of longitudinally opposed mass areas integrally connected to the longitudinal outer limits of said connect-ing legs.

4. A transducer lamination, comprising a single clongated generally rectangular sheet of ferromagnetic material having two longitudinally spaced symmetrically located winding openings therein, said sheet having an open elongated flux gap communicating with both Winding openings, thereby defining a pair of transversely opposed mass areas including the poles of said gap, said lamination being slotted partiaily transversely at symmetrically disposed locations longitudinally between said winding openings and the respective longitudinal limits of said lamination; thereby defining, between the slots and winding openings, integral connecting legs between the outer limits of said mass areas; and thereby also defining, longitudinally outside said slotted openings, a pair of longitudinally opposed mass areas integrally connected to the longitudinally outer limits of said connecting legs.

5. A transducer lamination, comprising a single elongated sheet of ferromagnetic material having two longitudinally spaced and symmetrically located winding openings therein, said sheet having a thin longitudinally extending open flux gap communicating with both winding openings, thereby defining two iiux-loop paths for circulation respectively about said winding openings and through adjacent portions of said gap, the longitudinal extent of said gap being substantially twice the minimum effective width of one of said paths.

6. A transducer lamination, comprising a single elongated sheet of ferromagnetic material having two longitudinally spaced and symmetrically located winding openings therein, said sheet having a thin longitudinally extending open flux gap communicatingl with both winding openings, thereby defining two flux-loop paths for iiux circulation respectively about said winding openings and through adjacent portions of said gap, the minimum effective width of each of said flux paths being at least one-half the effective longitudinal extent of said gap.

7'. A transducer lamination, comprising a single elongated gcnerally rectangular sheet of. ferromagnetic material having two longitudinally spaced symmetrically located Winding openings therein, said sheet having an open elongated linx gap communicating withboth winding openings, thereby defining a pair of transversely opposedV mass areas including 'the poles of said gap, said lamination being slotted partially transversely at symmetrically disposed locations longitudinally between said winding openings and the respective longitudinal limits of said lamination; thereby defining, between the slots and winding openings, integral transversely extending connecting legs between the outer limits of said mass areas; and thereby also defining, longitudinally outside said slotted openings, a pair of longitudinally opposed mass areas integrally connected to the longitudinally 4outer limits of said connecting legs; said transverse slots extending from the transverse outer limits of said lamination to define necks of limited width connecting said longitudinally opposed mass areas to said connecting legs.

8. A lamination according to claim 7, in which the effective width of each said neck is approximately one- `third the width of said lamination.

9. A lamination according to lclaim 7, in which the longitudinal extent of each said neck is of the order of the transverse width of each said neck, whereby each said neck may provide a longitudinally resilient connection of said longitudinally opposed mass areas to said connecting legs.

l0. A lamination according to claim 7, having an asymmetrically located reference opening in one of said longitudinally opposed mass areas.

11. A transducer lamination, comprising an integral single sheet of ferromagnetic material cut to define two transversely opposed mass areas, two longitudinally opposed mass areas symmetrically placed with respect to said transversely opposed mass areas, spring means connecting said longitudinally opposed mass areas to each other and via said transversely opposed mass areas, said transversely opposed mass areas being closely transversely spaced and defining therebetween an elongated llux gap.

12. A transducer lamination, comprising an integral single sheet of ferromagnetic material and cut to define two transversely opposed mass areas, two longitudinally opposed mass areas symmetrically located with respect to said transversely opposed mass areas, spring means connecting said transversely opposed mass areas to each other via said longitudinally opposed mass areas, said transversely opposed mass areas being closely transversely spaced and defining therebetween an elongated uX gap.

13. A transducer lamination, comprising an integral single sheet of ferromagnetic material and cut to define two transversely opposed mass areas, two longitudinally opposed mass areas symmetrically located with respect to said transversely opposed mass areas, spring means connecting said transversely opposed mass areas to each other with a central spacing between said transversely opposed mass areas defining an elongated flux gap, and means connecting said longitudinally opposed mass areas to said respective spring means.

No references cited. 

